384 Reports & Proceedings — Geological Society of London. 



1891 had proved the existence of certain lines and centres of 

 disturbance, but those authors observed that " the magnetic indica- 

 tions appear to be quite independent of the disposition of the newer 

 strata ", and he (the speaker) had not been able to detect any- 

 obvious connexion with the form and structure of the Palaeozoic 

 rocks below. In 1914-15 a new magnetic survey was made by 

 Mr. G. W. Walker, who confirmed the existence of certain areas of 

 disturbance. It was suggested that the effects might be due to 

 concealed masses of iron-ore, and the matter was referred to the 

 Conjoint Board of Scientific Societies, who appointed an Iron-Ores 

 Committee to consider what further steps should be taken. The 

 Committee recommended that attention should be concentrated on 

 certain areas of marked magnetic disturbance, and that a more 

 detailed magnetic survey of these areas, accompanied by a petro- 

 logical survey and an examination of the magnetic properties of the 

 rocks of the neighbourhood, should be made. He (the speaker) had 

 been approached with a view to the petrological work being under- 

 taken by the Geological Survey, and it had been arranged by the 

 Board of Education, with the consent of H.M. Treasury, that a 

 geologist should be temporarily appointed as a member of the staff 

 for the purposes of the investigation. Dr. Cox had received the 

 appointment, and the lecture which he was about to deliver would 

 show that results of great significance had been obtained by him. 

 The new magnetic observations had been made by Mr. Walker, and 

 the examination of the specimens collected, in regard to their 

 magnetic susceptibility, had been conducted by Prof. Ernest Wilson. 



Dr. Cox then described the selected areas, which lay on Lias and 

 Keuper Marl between Melton Mowbray and IS'ottingham, and in 

 the neighbourhood of Irthlingborough, where the !N"orthampton 

 Sands are being worked as iron-ores. The Middle Lias iron-ores, 

 consisting essentially of limonite, which crop out near Melton 

 Mowbray, have been proved incapable, by reason of their low 

 magnetic susceptibility, of causing disturbances of tlie magnitudes 

 observed, while the distribution of the disturbances showed no 

 correspondence with the outcrop of the iron-ores. Nor was any 

 other formation among the Secondary rocks found capable of exerting 

 any appreciable influence. It appeared, therefore, that the origin 

 ot the magnetic disturbances must be deep-seated. 



Investigation showed that the disturbances were arranged along 

 the lines of a system of faults ranging in direction from north-west 

 to nearly west. The faults near Melton Mowbray have not been 

 ])roved in the Palaeozoic rocks, and, so far as their effects on the 

 Secondary rocks are concerned, they would appear to be only minor 

 dislocations. But farther north, near Nottingham, faults which 

 take a parallel course, and probably belong to the same system 

 of faulting as those near Melton Mowbray, are known from evidence 

 obtained in underground workings to have a much greater throw in 

 the Coal-measures than in the Permian and Triassic rocks at the 

 surface. It appears, therefore, that movement took place along the 

 same lines at more than one period, the earlier and more powerful 

 movement being of post-Carboniferous but pre-Permian age, the- 



